Improve FAN control for ODROID-U3 - linux 3.8.13

odroid-u3_fan.patch

--- linux/drivers/hardkernel/odroidu2_fan.c	2014-09-06 15:18:25.000000000 +0900
+++ new/drivers/hardkernel/odroidu2_fan.c	2014-10-02 22:51:30.977219061 +0900
@@ -291,6 +291,8 @@
 {
 	struct odroid_fan *fan = container_of(work, struct odroid_fan, work.work);
 	unsigned long temperature;
+	int hysteresis = fan->duty ? 2 : 0;	// FAN off under start_temp - 2C
+	int duty, spinup = 0;
 	
 	/* check if its in auto-mode */
 	if(!fan->auto_mode)
@@ -300,7 +302,9 @@
 	
 	mutex_lock(&fan->mutex);
 	
-	if(temperature < fan->start_temp) {
+	if(temperature < 41)
+		hysteresis /= 2;		// FAN off under start_temp - 1C
+	if(temperature + hysteresis < fan->start_temp) { // avoid FAN on/off frequently
 		pwm_disable(fan->pwm);
 		pwm_config(fan->pwm, 1, fan->period);
 		pwm_enable(fan->pwm);
@@ -316,19 +320,45 @@
 	/* 83C is the first throttle.. 
 	 * Lets not reach it
 	 */
-	fan->duty = 255 * (temperature - fan->start_temp) / (FAN_TEMP_THROTTLE - fan->start_temp);
+/*
+               42+20=62C +----- 255 (max)
+                        /
+                       /
+                      /
+                     /
+  start_duty +------+
+             |     42C
+     0 ------+    
+        start_temp
+*/
+#define THRESHOLD_TEMPERATURE 42
+#define VARIABLE_RANGE 20
+
+	if(temperature <= THRESHOLD_TEMPERATURE)
+		duty = fan->start_duty;
+	else if(temperature >= THRESHOLD_TEMPERATURE + VARIABLE_RANGE)
+		duty = 255;
+	else {
+		duty = (temperature - THRESHOLD_TEMPERATURE)
+			* (255 - fan->start_duty) / VARIABLE_RANGE
+				+ fan->start_duty;
+	}
 	
 	/* Check if duty is lower than start_duty.
 	 * If yes, set it to start_duty.
 	 * Lets the user set an at least value for duty.
 	 */
-	if(fan->duty < fan->start_duty) {
-		fan->duty = fan->start_duty;
+	if(duty < fan->start_duty) {
+		duty = fan->start_duty;
 	}
 
+	if(fan->duty < 1 && duty > 1 && duty < 112)
+		spinup = 16;	// if FAN doesn't spin up, increase the value.
+
+	fan->duty = duty;
 	if(fan->pwm_status) {
 		pwm_disable(fan->pwm);
-		pwm_config(fan->pwm, fan->duty * fan->period / 255, fan->period);
+		pwm_config(fan->pwm, (duty + spinup) * fan->period / 255, fan->period);
 		pwm_enable(fan->pwm);
 	}
 	
@@ -375,7 +405,8 @@
 	
 	fan->pwm_status = 1;
 	fan->auto_mode = true;
-        fan->start_duty = 127;
+        fan->start_duty = 64;	// adjust you like
+        fan->start_temp = 32;	// almost FAN ON.
         	
 	mutex_init(&fan->mutex);